A conventional loudspeaker will be described with reference to FIG. 16. FIG. 16 is a cross-sectional view illustrating a conventional loudspeaker.
As shown in FIG. 16, magnetized magnet 1 is coupled to lower plate 3 having center pole 3A and a side of magnet 1 opposite to the side coupled to lower plate 3 is coupled to upper plate 2 to constitute external magnetization-type magnetic circuit 4. Magnetic circuit 4 is coupled to frame 6. A periphery of frame 6 is coupled to diaphragm 7. Diaphragm 7 is coupled to voice coil 8. Voice coil 8 is inserted to magnetic gap 5 of magnetic circuit 4, thereby constituting a loudspeaker.
This conventional loudspeaker has an overall height structure using a so-called buildup method in which magnetic circuit 4 is coupled to frame 6. Due to this structure, the conventional loudspeaker has required, at minimum, an overall height obtained by adding a size of magnetic circuit 4 to a size of frame 6.
Recently, flat-screen televisions (e.g., liquid crystal televisions, plasma televisions) are more prevalent in the field of AV products, resulting in the recent rapid increase in requirements for a smaller overall height of a loudspeaker. The mobile product field also shows requirements for a mobile phone having multiple functions and a thinner size, showing very strong requirements for a thinner loudspeaker. On the other hand, the in-vehicle application field also shows very strong requirements for a smaller, thinner, and more lightweight loudspeaker involved with energy conservation to protect the global environment.
Due to these backgrounds, more conventional loudspeakers as described above have been developed to satisfy such requirements for a smaller, thinner, and more lightweight loudspeaker.
Because of the circumstance as described above, there is already a limitation on realizing both of the structure of the conventional loudspeaker and a thinner size while satisfying the market demands. Thus, a new revolutionary structure is required for a loudspeaker, resulting in particular in the recent enhanced development for realizing a loudspeaker having a thinner size. Information for publications for the related art regarding this application includes Patent Publication 1 for example.
As described above, the conventional loudspeaker is disadvantageous in that there is already a limitation on realizing both of the conventional loudspeaker structure and a thinner size while satisfying the strict market demands. Furthermore, there are other demands from the market for a loudspeaker to have an improved conversion efficiency for the purpose of energy conservation and a further improved sound pressure level.
In order to cope with these requirements, only options are to use a magnet having a large volume or to add a cancel magnet to constitute a repulsive magnetic circuit to efficiently use the magnetic energy of the magnet.
Any of the options cannot avoid an increased volume of a magnetic circuit including a magnet, showing a further difficulty in realizing a thinner size.
[Patent Publication 1] Japanese Patent Unexamined Publication No. 2005-51283